Flash assisted annealing

ABSTRACT

The present disclosure relates to a rapid thermal processing system that may be useful for processing semiconductor devices. A flash lamp may be utilized to provide pulse heating of a semiconductor for annealing or other purposes. A sensor may be provided to sense a characteristic of a semiconductor when a pre-pulse is applied to the semiconductor. Subsequent pulses may then be adjusted based on the characteristic sensed by the sensor.

FIELD OF THE INVENTION

[0001] This disclosure relates to semiconductor rapid thermalprocessing. In particular this disclosure relates to annealingsemiconductor wafers and other semiconductor devices.

BACKGROUND

[0002] Many individual process steps are required to produce asatisfactory semiconductor transistor. One such process is the annealingprocess wherein the temperature of the semiconductor die or wafer, asthe case may be, is brought to a sufficient elevated temperature for theannealing process to be effective. However, there are many variations insemiconductor devices such as die layout and film stack variations,which tend to make each semiconductor device, die layout and film stackrespond differently than previous and subsequent devices.

[0003] For example one wafer may contain a plurality of sections each ofwhich may become a microprocessor in subsequent processing. Whileanother wafer may contain areas that may become flash memory devices insubsequent processing stages. Therefore, as between the two wafers,there may be a multitude of variations in patterns, number of layers,and other differences. These differences may result in each waferrequiring more or less energy to achieve an adequate annealingtemperature.

[0004] These variations are particularly troublesome with flash assistedannealing in the sub-melt regieme for silicon. In the flash annealprocess, a high intensity lamp is utilized to inject thermal energysufficient to achieve the annealing process quickly enough to heat onlythe surface of the wafer and not the bulk. The final peak surfacetemperature is a critical parameter of the system. Too much energy canmelt the transistors. However, the changes in wafers as discussedpreviously may result in differences of reflectivity of the surfacesthat can significantly affect the peak surface temperature achieved inthe process. Also, variations in the amount of light originating fromthe flash lamp system also lead to unacceptable variations in the peaksurface temperature.

[0005] Therefore, what is needed is a method and apparatus forcontrolling the flash anneal process and other improvements insemiconductor processing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a block diagram of a flash annealing process accordingto embodiments of the present invention;

[0007]FIG. 2 is a block diagram of a flash annealing process usingfrontside semiconductor monitoring according to embodiments of thepresent invention;

[0008]FIG. 3 is a graph of wafer temperature v. time of a semiconductordevice according to embodiments of the present invention;

[0009]FIG. 4 is a graph of the temperature v. time of the backside of asemiconductor device according to embodiments of the present invention;

[0010]FIG. 5 is a graph of temperature v. time of a semiconductor deviceaccording to embodiments of the present invention;

[0011]FIG. 6 is graphs of temperature v. time for a wafer anneal processaccording to embodiments of the present invention;

[0012]FIG. 7 is a flow chart of an annealing process according toembodiments of the invention; and

[0013]FIG. 8 is a surface temperature vs. time chart according toembodiments of the invention.

DETAILED DESCRIPTION

[0014] Referring now to FIG. 1, a flash lamp 101 is coupled to a flashcontroller 103. The flash controller 103 is also coupled to a feedbackcircuit 105 that is in turn coupled to a semiconductor temperaturesensor 107.

[0015] The flash 101 may be any suitable flash device such as an arclamp, laser light generator or other light source that is capable of thepower output on a time scale shorter than required for heat to diffusefrom the front surface of the wafer to the backside. The flash lamp 101illuminates wafer 109 such that the temperature of the surface of wafer109 is elevated. In this context, wafer shall be used in a broadly tocover a wafer, die or other semiconductor device. The degree of thermalelevation may be detected by temperature sensor 107 which may beprocessed by feedback circuit 105. The feedback circuit 105 may thenprovide a signal to the flash controller 103 such that the duration offlashes, number of flashes, or combinations of duration and number offlashes may be adjusted as required by a particular wafer for effectiveannealing. In some embodiments, the temperature sensor 107 may monitorthe temperature of the backside of the wafer 109 where the frontside ofwafer 109 is a surface, which is being annealed. The flash 101 may beconfigured such that it is isolated from a processing chamber (notshown) by a glass or quartz window 111.

[0016] Referring now to FIG. 2, flash 101, flash controller 103,feedback 105 and wafer 109 may be as described previously. However,sensor 201 may be operative, in some embodiments, to monitor thefrontside of wafer 109. Again, the frontside of wafer 109 is the sidethat may be subjected to the annealing process. The sensor 201 maymonitor a number of parameters of the frontside of the wafer, forexample, the wafer monitor 201 may detect the reflectivity of thesurface of one or more areas of wafer 109. In other embodiments, wafermonitor 201 may monitor the surface temperature of one or more areas ofthe frontside of wafer 109. Alternatively, the sensor may monitor boththe reflectivity and temperature of the wafer 109.

[0017] In a flash assist annealing process, the wafer bulk may beelevated to a preset temperature or temperature range after which theflash, such as flash 101, may then be pulsed to elevate the surfacetemperature of the wafer to a target temperature or temperature range.Either the backside temperature of the wafer or the surface temperatureof the wafer may be utilized, in some embodiments, to determine thewafer temperature before the flash anneal pulses, and the effect of theflash anneal pulses, on the wafer.

[0018] Referring now to FIG. 3, a temperature vs. time graph of a waferaccording to some embodiments of the present invention is illustrated.The temperature of the wafer such as wafer 109 is elevated to a floortemperature range 301. In some embodiments, this range may betweenapproximately 300 and 1000 degrees centigrade. This may be considered anintermediate temperature. After the wafer has risen to the intermediatetemperature, in some embodiments, a monitor pulse 303 is produced. Thispulse may be produced by flashing a lamp such as an arc lamp 101. Themonitor pulse may be controlled such that it is at a reduced amplitudesuch that it will not to exceed a critical surface temperature jump thatwould affect transistor processing. The effect of this first pulse, thatmay be considered a pre-pulse, may be utilized to determine thereflectivity of one or more areas of the wafer. In other embodiments,the pre-pulse may be utilized to determine the temperature rise of thesurface of the wafer from the pre-pulse.

[0019] By monitoring the effect of the pre-pulse on the surface of thewafer, the feedback circuit such as circuit 105 may generate a signalthat may be utilized by the flash control 103 to control the amplitudeof the subsequent flash pulse to achieve the desired annealing affect.This process can be repeated iteratively if the system is configured torun multiple pulses in the wafer process. Each subsequent pulse can bemodulated based on the prior pulse if there is a long term drift to thesystem. If there is a degree of variability in the pulse amplitude, thenmultiple pulses can be run to achieve improved control of the averageenergy deposited in the system. In some embodiments, the targettemperature for annealing may be approximately 1300 degrees centigradefor a period, which may be between approximately 0.1-5.0 milliseconds.For the above mentioned reasons, pulses 305-307 may be utilized to raisethe surface temperature of the wafer to the desired annealingtemperature.

[0020] Referring now to FIG. 4, the measurement of the backside of awafer, such as wafer 109, during a flash assisted annealing process maybe represented by the graph line 401, depending on the spacing of thelight pulses. As illustrated, immediately following the flash pulse,there is no increase in the surface temperature on the backside. As thesurface temperature of the silicon begins to equilibrate with the bulk,the backside temperature rises until point 403 when it is in equilibriumwith the surface. The period between point 403 through approximatelypoint 405 may represent the temperature of the backside of the wafer asa result of a flash pulse on the frontside of the wafer. Thus pulse (notshown) may generate a temperature peak at point 407 at which point thetemperature of the wafer may decrease to point 405. The bulk temperaturejump as indicated by point 407 is the best measure of the total energydeposited in the system and is the quantity used to feed back to thecontroller the magnitude of the adjustment of the subsequent pulse. Theperiod from points 405 to 409 may represent the result of a second flashpulse on the frontside of the wafer. Typically, in some embodiments,multiple peaks will occur as multiple flash pulses are utilized toanneal of the wafer.

[0021] If the system has the wafer on a hot plate, backside temperaturemeasurement is may not possible. In this configuration, the surfacetemperature may be used as the control quantity. The processing sequencemay be as follows: Place wafer on hot plate ex ˜500C. for a few seconds.Adjust surface pyrometer (temperature) to 500C. since this quantity isnow known. It may not be enough to be able to measure the emmisivityonly at 500C. because it is a function of temperature and varies withmaterial type (i.e., silicon nitride or polysilicon, etc . . . ). Thequantity of interest, in some embodiments, is the emmisivity from theintermediate temperature to the peak temperature since this is whatcontrols the final peak temperature.

[0022] Flash wafer surface to approximately 1300 c with the lamp. Duringthis flash process, the light from the flash lamp may dominate thesignal from the photodetector. Measure the light intensity with time tomeasure the lamp time profile which can be used as a monitor of thelight pulse intensity and deconvolute this with the wafer emmisivity.The flash pulse should last no longer than a few milliseconds. As thehot surface equilibrates with the bulk wafer (˜20 milliseconds), thebulk temperature rise is on the order of ˜50C. which will cool down on atime frame of about 1 second. This bulk temperature rise will appear asa discontinuity on the second time frame if you draw the flash lampprocess on the same time scale. This magnitude of the bulk temperaturerise is the quantity which will indicate the peak surface temperature ifwe know the pulse profile and is the control quantity of interest.

[0023] Referring now to FIG. 5, in some embodiments, it may be desirableto measure wafer reflectivity with the wafer at approximately roomtemperature. While at approximately room temperature, a pre-pulse 501may be utilized to measure the reflectivity of the wafer 109. After thereflectivity is measured, the wafer may be brought up to an intermediatetemperature such as at point 503. After the wafer has reached anintermediate temperature, then a flash pulse such as a pulse atapproximately point 505 may be triggered to increase a surfacetemperature to the desired level. After one or more pulses such asoccurs at time 505, the wafer is allowed to cool back to anapproximately room temperature such as represented by point 507. Asbefore, the pulses such as occurs at point in time 505 may be adjustedbased on the feedback of reflectivity from the pulse that occurred atpoint 501.

[0024] Referring now to FIG. 6, the wafer may be brought up to a lowintermediate temperature. Once the low intermediate temperature has beenreached by the wafer, a pre-pulse such as may occur at point 603 may betriggered. After the pre-pulse has occurred, the wafer may then be takenup to an intermediate temperature 605 thereupon one or more flash pulsesmay be utilized as described before to anneal the wafer. In thisexample, the results of pre-pulse 603 may be utilized to control theduration and/or the number of subsequent pulses that may occur once thewafer has reached approximately an intermediate temperature.

[0025] Referring now to FIG. 7, in some embodiments, a pre-pulse 701 isapplied to a wafer. The result of the pre-pulse is sensed 703 andutilized to adjust subsequent pulses 705. The adjustments may be asdescribed above. Then, in some embodiments, additional pulses are thenutilized to anneal the wafer 707.

[0026] Referring now to FIG. 8, in some embodiments, a flash pulse attime 801 is triggered that increased the surface temperature of a wafer.A short time there after, such as at point of time 803, the surfacetemperature has substantially decreased. The surface temperature of thewafer continues to decrease as indicated at time 805.

[0027] In the above described embodiments, the effect of the pre-pulseon the wafer may be detected by a temperature sensor or reflectometermonitoring the upper surface being annealed or, in other embodiments,may be monitored by a temperature sensor monitoring the temperature ofthe backside of the wafer. As was previously described, the results ofthe pre-pulse may be utilized to control subsequent flash pulses thatmay then be utilized to anneal the frontside of a wafer such as wafer109. This adjustment of subsequent pulses by monitoring the result of apre-pulse may be utilized, in some embodiments, to compensate forchanges in the flash lamp such as lamp 101 due to age or other factors.In addition, this adjustment of the flash pulses may be utilized, asdescribed before, to compensate for wafer-to-wafer differences.

[0028] While the present invention has been described with respect to alimited number of embodiments, those skilled in the art will appreciatenumerous modifications and variations there from. It is intended thatthe appended claims cover all such modifications and variations as fallwithin the true spirit and scope of this present invention.

What is claimed is:
 1. An apparatus comprising: a pulse heat sourcecoupled to heat an object within a processing chamber; a pulse heatsource controller coupled to the pulse heat source; and a sensor coupledto the pulse heat source controller and operative to generate a signalrelated, in part, to a parameter of an object within the processingchamber and the pulse heat source controller controls the pulse heatsource, in part, in response to the signal from the sensor.
 2. Theapparatus as in claim 1, wherein the pulse heat source is a lamp.
 3. Theapparatus as in claim 2, wherein the lamp is an arc lamp.
 4. Theapparatus as in claim 2, wherein the lamp is a Laser light genrator. 5.The apparatus as in claim 1, wherein the sensor generates a signalrelated, in part, to the reflectivity of an object within the processingchamber
 6. The apparatus as in claim 1, wherein the sensor generates asignal related, in part, to the temperature of an object within theprocessing chamber
 7. The apparatus as in claim 6, wherein the sensorgenerates a signal related, in part, to the temperature of a frontsidesurface of an object within the processing chamber wherein the objecthas a frontside and a backside surface
 8. The apparatus as in claim 6,wherein the sensor generates a signal related, in part, to thetemperature of a backside surface of an object within the processingchamber wherein the object has a frontside and a backside surface
 9. Theapparatus as in claim 1, wherein the pulse heat source controllercontrols the number of pulses of the pulse heat source, in part, inresponse to the signal from the sensor.
 10. The apparatus as in claim 1,wherein the pulse heat source controller controls the duration of atleast one pulses of the pulse heat source, in part, in response to thesignal from the sensor
 11. The apparatus as in claim 1, wherein thepulse heat source controller controls the number of pulses of the pulseheat source based, in part, in response to the signal from the sensorgenerated, in part, in response to a pre-pulse.
 12. The apparatus as inclaim 1, wherein the pulse heat source controller controls the durationof at least one pulse of the pulse heat source based, in part, inresponse to the signal from the sensor generated, in part, in responseto a pre-pulse
 13. A method comprising: sensing a parameter of an objectheated within a processing chamber with a first pulse from a pulse heatsource; and heating the object with additional pulses from the pulseheat source based, in part, on the sensed parameter of the object 14.The method of claim 13, wherein sensing a parameter of the objectincludes sensing the temperature of the object having a frontside and abackside
 15. The method of claim 14, wherein sensing a parameter of theobject includes sensing the temperature of the frontside of the object16. The method of claim 14, wherein sensing a parameter of the objectincludes sensing the temperature of the backside of the object.
 17. Themethod of claim 13, wherein sensing a parameter of the object includessensing the reflectivity of the object
 18. The method of claim 13,heating the object with additional pulses from the pulse heat sourceincludes heating the object with pulses from a lamp
 19. A systemcomprising: a processing chamber; a pulse heat source coupled to heat anobject within the processing chamber; a pulse heat source controllercoupled to the pulse heat source; and a sensor coupled to the pulse heatsource controller and operative to generate a signal related, in part,to a parameter of an object within the processing chamber and the pulseheat source controller controls the pulse heat source, in part, inresponse to the signal from the sensor.
 20. The apparatus as in claim19, wherein the pulse heat source is a lamp
 21. The system as in claim19, wherein the sensor generates a signal related, in part, to thereflectivity of an object within the processing chamber
 22. The systemas in claim 19, wherein the sensor generates a signal related, in part,to the temperature of an object within the processing chamber whereinthe object has a frontside and a backside
 23. The system as in claim 22,wherein the sensor generates a signal related, in part, to thetemperature of the backside of the object within the processing chamber24. The system as in claim 22, wherein the sensor generates a signalrelated, in part, to the temperature of the frontside of the objectwithin the processing chamber
 25. The system as in claim 22, wherein thesensor generates a signal related, in part, to a pre-pulse of the pulseheat source